Table 1

Summary of studies in systematic review.

Author	Study type	Country	Data source	Years of study	Age group, yr	No. of patients	Age, yr, mean ± SD
O’Connell et al., 2003 (11)	Retrospective	US	SEER	1991–1999	20–40	466	34.1 ± 4.5
O’Connell et al., 2003 (11)	Retrospective	US	SEER	1991–1999	60–80	11 312	70.0 ± 5.5
O’Connell et al., 2004 (12)	Retrospective	US	SEER	1991–1999	20–40	1334	34.1 ± 4.4
O’Connell et al., 2004 (12)	Retrospective	US	SEER	1991–1999	60–80	46 457	70.8 ± 5.4
Wang et al., 2010 (13)	Retrospective	US	SEER	1992–2006	< 40	2642	—
Wang et al., 2010 (13)	Retrospective	US	SEER	1992–2006	≥ 40	138 769	—
McKay et al., 2014 (27)	Retrospective	Canada	Manitoba Cancer Registry	2004–2006	< 45	70	38.0 ± 4.8
					45–79	1459	66.0 ± 9.2
					≥ 80	557	85.0 ± 4.1
Kneuertz et al., 2015 (18)	Retrospective	US	NCDB	2003–2005	18–49	13 102	—
Kneuertz et al., 2015 (18)	Retrospective	US	NCDB	2003–2005	65–75	37 007	—
Wang et al., 2015 (14)	Retrospective	US	SEER	1998–2011	20–40	6700	34.9 ± 4.6
					41–50	19 385	46.5 ± 2.8
					> 50	253 538	72.0 ± 10.5
Abdelsattar et al., 2016 (10)	Retrospective	US	SEER	1998–2011	< 50	37 847	42.5 ± 6.0
Abdelsattar et al., 2016 (10)	Retrospective	US	SEER	1998–2011	≥ 50	220 177	65.3 ± 8.5
Wolbert et al., 2018 (26)*	Retrospective	US	Cabell Huntington Hospital Registry	2003–2016	< 50	24	43.1
Wolbert et al., 2018 (26)*	Retrospective	US	Cabell Huntington Hospital Registry	2003–2016	≥ 50	113	64.0

NCDB = National Cancer Database Centre; SD = standard deviation; SEER = Surveillance; Epidemiology and End Results; US = United States.
* Standard deviations were not available for this study.